Conventional control panels having control elements, for example having pushbutton switches or display elements in house doorbells, transport means, elevators, etc., envisage that one or more control elements are fastened to a front panel or introduced into said panel and the latter in turn can be fastened in the desired place. In the installation of such control panels, the control elements are fastened to the front panel in a first step, which can be effected, for example, by means of a screw nut which is screwed onto a thread provided on the control element. The front panel as a whole is then fastened. However, such a procedure does of course require that the front panel be prefabricated as a separate workpiece. The installation, too, can be inconvenient and tedious depending on the cabling of the control elements and depending on accessibility of the control panel. Moreover, the front panel must be detached as a whole if a control element is faulty.
It would therefore be desirable to be able to fasten a control element directly to an already installed front panel. Such a front panel then need not be a separate, prefabricated workpiece. It would also be entirely possible for the casing provided with suitable openings, the housing or the like of the article on which the control panel is to be mounted also to serve directly as the front panel. In this way, high costs both for the production of the control panel and for its installation would of course be saved. A known means for permitting the fastening of a control element to a front panel installed in a fixed position consists in providing the front panel with additional holes into which, for example, plastics arms provided with a sawtooth profile and mounted on the control element can be introduced, which arms then fix the control element to the front panel. An other solution is disclosed in the two U.S. Pat. Nos. 4,070,559 and 4,016,359. These two publications each disclose a control element which can be formed, for example, as a switch or lever or as an electrical insulator and can be fastened to a front panel with a circular opening. In these known cases, the control element has a housing with a cylindrical section and an annular groove running all round the cylindrical section. The cylindrical section is dimensioned so that it fits virtually without play into the circular opening. These known control elements furthermore each have an annular spiral spring which fits into the annular groove and serves for fastening the control element without additional fastening means, i.e. in the manner of a snap fastener, to the front panel. On insertion of the control element into said front panel, the spiral spring is pressed into the annular groove. It relaxes again in the inserted state and then rests against the inside of the front panel, with the result that the control element is fixed in the opening.
This known method of fastening has the disadvantage that the cylindrical section has to be dimensioned so exactly that it can be inserted into the opening of the front panel so that it fits tightly, i.e. without play, and that the control element is relatively expensive because the spiral spring has to be specially made for this purpose.